Perhaps due to unique structural features of the Y chromosome, conventional gene targeting strategies in mouse embryonic stem cells to generate mutations on the Y-linked genes have had limited success. Therefore, often the understanding of the functions of murine P-linked genes is limited to insights gained from studies of mice that carry spontaneous deletions, random gene traps insertions or autosomal transgenes. Methods are needed to improve the ability to target a genomic locus on the Y chromosome.
The Sry protein (sex-determining region Y) is the key regulator of male sex determination in placental mammals. The Sry gene, also known as the Testis Determining Factor (TDF), resides on the Y chromosome. Sry is thought to be a transcription factor that binds DNA through its High Mobility Group (HMG) domain. Expression of the mouse Sry gene is restricted to the genital ridge in a narrow time window around day 11 of embryonic development; both Sry mRNA and protein are detected. Sufficient Sry must be made within this time window to convert the bipotential genital ridge toward the male testis forming program while inhibiting the female program of ovary development. In adult testes a circular Sry transcript is detected but not the Sry protein. Mutations in the Sry gene that cause the production of an inactive Sry protein or that alter the timing and strength of gene expression can cause male to female sex reversal, resulting in animals that have an X and a Y chromosome but are anatomically female. So-called XY females are often sterile or have a low fertility. Being able to control sex determination by regulation of the Sry would have great value in the production of genetically modified animals.